Many conditions, e.g., trauma, tumor, disease, are known to cause the brain to swell, increasing intracranial pressure. In many situations this increase in ICP may be life threatening, requiring a surgical procedure known as a decompressive craniotomy. In this procedure, a large segment of cranial bone, known as the bone flap, is removed from the cranium. The removal of the bone flap relieves the intracranial pressure by allowing the brain to temporarily swell through the hole made in the cranium.
The bone flap is stored, with the intent of returning it to the cranium, once the swelling has subsided and the patient has stabilized, typically 4-6 weeks after the procedure. The bone flap is stored either by surgically inserting it into the abdomen, or by freezing it. By the time the bone flap is to be surgically returned, it often is no longer a viable specimen either due to changing of shape/composition, i.e., remodeling, while in the abdomen or by failing culture tests. In these situations, there are three options available to the surgeon.
One option is fabrication of a custom helmet to protect the affected area. This option is rarely employed.
A second option is the creation of a custom computer generated implant. The implant is attached to the cranium and the scalp is drawn back over the implant Typically the implant fits wonderfully. However, such implants are expensive and require 1 mm fine cut CT scan.
A third option is to use a titanium mesh to cover the hole where the bone has been removed. The mesh is formed from a flat sheet fabricated by the surgeon; or is formed from a prefabricated shape ordered from catalogue. As with the implant, the scalp is drawn back over the mesh.
Both the computer generated implants and titanium mesh solutions are known to have high failure rates. During the 4 to 6 week post-operative period a “dead space” or “void” will occur beneath the region where the bone flap was removed. The mesh may collapse into the void. Even if there is no collapse of the mesh, there is still a void between the brain and the mesh that may become an infection zone.
The cranium may be considered to be like a simple pressure vessel that is held in dynamic equilibrium through arterial (+) and venous (−) pressures and the brain may be considered to be like a sponge. Once the bone flap is removed from the cranium, the brain is exposed to atmospheric pressure that is greater than the intracranial pressure. The atmospheric pressure compresses the brain. The brain is only so elastic, and the rate at which it is compressed can lead to both reversible and irreversible neurological impairment (e.g., loss of speech, mobility upon arising in the morning) and tearing of the nerve fibers.
Accordingly, it is desirable to provide a method and apparatus to protect intracranial contents from the effects of atmospheric pressure.